Field of the Invention
The invention relates to a process for producing structured coatings. The invention especially relates to a process for producing optically dense, thermally stable, nonconductive, structured coatings. The present invention likewise relates to the structured coatings producible by the process according to the invention.
Discussion of the Background
Structured coatings are of significance for many technical fields of use. Optically dense, nonconductive structured coatings are essential for many applications in semiconductor technology. Especially for the production of displays, optically dense, nonconductive coatings are required, in order to frame the edge of the display, protect electronic components from light and/or serve for pixel separation of the colour filters. The coating which achieves the above objects—since they often lead to black coatings—is referred to as black matrix. However, they may in principle have any desired colour. Preferably, black matrices, however, are black or white.
The prior art discloses various processes for producing structured coatings, especially for producing black matrices.
EP 0 762 996 A1 discloses a process for producing structured coatings, in which the structuring is produced by embossing tools. However, this process is not applicable to finely structured coatings as required, for example, in semiconductor technology.
For example, black matrices can also be produced by deposition of chromium, especially via sputtering (EP 0 740 183 A1). However, this method has the disadvantage that corresponding processes are very complex in apparatus terms and require large constructions, and integration into processes for producing displays is very complex. A further disadvantage of the use of chromium is that it is a heavy metal and hence environmentally harmful, and is very costly to dispose of.
Structured coatings or black matrices can also be produced in principle via colouring with an organic dye (EP 0 740 183 A1). However, coating compositions comprising an organic dye are unsuitable for achievement of structured coatings having a high colour depth and homogeneous colour distribution. Black coatings in particular cannot be produced with these solutions, since there are no organic dyes to date that lead to deep black coatings. Coating compositions comprising mixtures of different dyes also have the disadvantage of leading to inadequate colour depth. An additional result is disadvantageous inhomogeneous colourings. Coatings comprising organic dyes are also incapable of withstanding temperatures as often used in display production. For this reason, solutions comprising organic dyes have not led to any commercial use to date in display production.
Customary printing methods which use coating compositions comprising colouring agents that are not organic dyes still cannot be used to date to produce sufficiently finely structured coatings and especially not sufficiently sharply bounded black matrices. One means of producing black matrices is based, for example, on the use of a coating composition comprising a binder and an inorganic pigment (EP 0 740 183 A1). The pigment used may be be carbon black (i.e. pigment black). However, carbon black is disadvantageous since corresponding coatings can become conductive. Alternatively, metal oxides, especially spinel colour pigments, are also used. Among these, particular preference is given to spinel colour pigments, since they can also be used to produce nonconductive coatings from coating compositions comprising high pigment concentrations. In addition, pigment blacks and many other pigments can be dispersed only with difficulty or have a tendency to coagulate, which again has an adverse effect on the quality of the black matrix layer. Finally, spinel pigments are very thermally stable and can—unlike pigment blacks and non-spinel pigments in some cases even not be formed until they are within the cured coatings (Silva et al., Journal of Magnetism and Magnetic Materials, 272-276 (2004) e 1851-e1853). The colour pigments may also be surface-treated (cf., for example, DE 40 14 928 C1 and U.S. Pat. No. 6,136,083 A). However, it is still not possible by the processes that use metal oxide pigments and are known to date to produce sufficiently finely structured coatings.
Finally, structured coatings or black matrices can also be produced by selective conversion of photosensitive coating compositions comprising a black pigment (for example carbon black). However, this process too leads to inferior coatings, especially because of incomplete conversion at high pigment contents. EP 0 740 183 A1 discloses a process for producing structured coatings, in which a coating composition comprising a black compound oxide pigment comprising at least two metal oxides, an inorganic binder and a photosensitive resin is applied to a substrate, and the coating composition applied is irradiated with a mercury vapour lamp through a photomask, developed, washed and optionally post-heated further. However, the use of photosensitive resins based on organic systems has the disadvantage that the layers produced using them cannot be exposed to the high temperatures that are advantageously used in display production.